A decent IDE / code-editor addon for blender
There is a paid add-on on Blender Market: Link, but the add-on is also available for free from GitHub here: https://github.com/JacquesLucke/code_autocomplete. You would just need to use the green "Clone or Download" button and choose to download it as a .zip. Note that Jacques Lucke says here:


  You can buy it in the BlenderMarket but it is also freely available on github.
  Buying the addon entitles you to better support when you have questions and helps to ensure that I can continue working on my addons!


And another free one: Link

Eclipse related: Link